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318 stunble

Posted By: '84 D150 Shorty

318 stunble - 04/30/10 04:23 AM

Just got the 318 running today, but got a small problem. At idle, it runs smooth with no miss, but if i move the throttle abrubtly, it stumbles or chokes briefly then catches up and revs up smoothly. if i move the throttle slowly it doesnt do this. what would cause that?
Posted By: RapidRobert

Re: 318 stunble - 04/30/10 04:28 AM

check for an immediate squirt of gas when you move the throttle & I'm assuming it's warmed up/choke off as inadequate choke closing can do it
Posted By: '84 D150 Shorty

Re: 318 stunble - 04/30/10 04:39 AM

Quote:

check for an immediate squirt of gas when you move the throttle & I'm assuming it's warmed up/choke off as inadequate choke closing can do it




k, i just checked that, and didnt see gas squirting in. a little bit of fuel is going, but i should be able to see a visible squirt of fuel goin in right? if so, what would cause that?
Posted By: RapidRobert

Re: 318 stunble - 04/30/10 04:42 AM

take the top off and check the acclerator plunger neoprene cup for rips/tears & if good check the float level (good idea anyway as it's easy and you have the top off)
Posted By: '84 D150 Shorty

Re: 318 stunble - 04/30/10 04:43 AM

okie doke. gonna do that now
Posted By: RapidRobert

Re: 318 stunble - 04/30/10 04:45 AM

I gotta hit the hay. I'll get w you tomorrow.
Posted By: '84 D150 Shorty

Re: 318 stunble - 04/30/10 05:43 AM

ok, checked the accelerator pump diaphram and adjusted the float level, same problem, but i noticed that if i held the choke partially closed, the stumble went away...any ideas?
Posted By: Evil Monkey

Re: 318 stunble - 04/30/10 06:42 AM

I'm no carburetor expert, but here's my thoughts. With no visible fuel squirt when you hit the accelerator, that means your accelerator pump is not working properly. Running with the choke partially closed will give you more fuel, so the accelerator pump issue will not be noticeable - you're covering up the lack of an accelerator pump squirt by introducing more fuel into the system with the choke. So, we need to determine why your accelerator pump is not squirting.

On my Holley, when you hit the accelerator, the accelerator pump cam pushes on a lever, which then pushes on the accelerator pump diaphram, which forces fuel through a passage and out of the squirter. A spring inside the accelerator pump bowl forces the diaphram back when the accelerator goes back to idle position. If the lever is sticking, the diaphram will not return, and the accelerator pump cam can move all it wants but it won't be moving the lever (since it's stuck), and you won't get a squirt. The same thing would probably happen if the spring behind the diaphram was broken - it wouldn't return the diaphram, and you would get no squirt. You may also have a plugged passage to the squirter, or a plugged squirter, or even a wiped lobe on the accelerator pump cam.

The way your carb creates the squirt may be different, but the principles should be the same - something pushes on the diaphram, causing fuel to flow through and out of the squirter. If the diaphram isn't being pushed, or it isn't returning, or the system is plugged, you won't get a squirt.
Posted By: 451Mopar

Re: 318 stunble - 04/30/10 08:08 AM

If it is an Edelbrock / Carter AFB/AVS type carb, check fuel bowl level as about to the level of the baffle inside the fuel bowl.
Posted By: patrick

Re: 318 stunble - 04/30/10 10:56 AM

what kind of carb?

if it's an edelbrock/carter, you can change the position of the linkage to a hole closer to the body of the carb, that'll give a larger pump shot, if the accelerator pump is working correctly. you should see a solid squirt when snapping the throttle.
Posted By: '84 D150 Shorty

Re: 318 stunble - 04/30/10 01:52 PM

The carb is a holley 2bbl, it is an older type (no oxygen feedback or other junk on it)
Posted By: RapidRobert

Re: 318 stunble - 04/30/10 01:56 PM

Quote:

what kind of carb?


idle it for a minute then pull the top off and as said the fuel level should be up to the slots in each float baffle in each side (eddy) then take off the AP plunger & plunge it into the well and see what you get for a squirt & if inadequate take off the squirter and see if the brass plunger w the pointed tip is in there & if so call your parts house and get another AP. If it's a leather one run a mini screwdriver around the inside perimeter between the leather and the spring to expand it a bit then slightly lube it & install. If a holley also see if the pointed needle is in place & if so take off the carb and the 4 bolts on the square AP metal cover and replace the pump diaphram
Posted By: '84 D150 Shorty

Re: 318 stunble - 04/30/10 01:56 PM

when i depress the accelerator lever, it doesnt quite feel right. it feels lose. im thinking if i was moving the lever, i should feel it making a slight suction, but i dont, and i am definitely not seing a solid squirt of fuel.
Posted By: RapidRobert

Re: 318 stunble - 04/30/10 09:50 PM

might take off the squirter & see if the brass valve is loose and move the throttle and see if it squirts and if not then I think the carb needs to come off to get at the AP diaphram under the square cover. I'm assuming that the external linkage is intact/moving, that it's something inside
Posted By: '84 D150 Shorty

Re: 318 stunble - 05/01/10 10:38 AM

ok, i figured it out yall! thank you all for your help! it turned out that indeed the problem was in the accelerator pump, specifically, the check ball was stuck (probably from sitting too long). i bought a rebuild kit from autozone for 20 bucks, and overhauled the top half of the carb while it was on the motor. Easy as pie! the carb is a holley 2280 2bbl. chrysler used this carb for many applications for small blocks. the check ball was under the squirter nozzle assembly, and i found instructions in my chrysler dealer repair manual specific to this carb model for testing of the accelerator pump and float adjustments. maybe this will help someone else!! the engine accelerates crisp and smooth now!
Posted By: RapidRobert

Re: 318 stunble - 05/01/10 03:08 PM

What was in there a ball or the pointed needle. I'm not a holley guy and one I have has just the needle
Posted By: '84 D150 Shorty

Re: 318 stunble - 05/02/10 02:40 AM

Quote:

What was in there a ball or the pointed needle. I'm not a holley guy and one I have has just the needle




it was a ball bearing type with a small weight above it. The bearing seals the opening, with the weight on top, in a bore located beneath the fuel nozzles
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